<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>* {
    margin: 0;
    padding: 0;
  }

  li {
    list-style-type: none;
  }

  a {
    text-decoration: none;
    font-size: 14px;
  }

  .nav {
    margin: 50px;
  }

  .nav>li {
    position: relative;
    float: left;
    width: 80px;
    height: 41px;
    text-align: center;
    border: 1px solid black;
  }

  .nav li a {
    display: block;
    width: 100%;
    height: 100%;
    line-height: 41px;
    color: #333;
  }

  .nav>li>a:hover {
    background-color: #eee;
  }

  .nav ul {
    display: none;
    position: absolute;
    top: 41px;
    left: 0;
    width: 100%;
    border-left: 1px solid #FECC5B;
    border-right: 1px solid #FECC5B;
  }

  .nav ul li {
    border-bottom: 1px solid #FECC5B;
  }

  .nav ul li a:hover {
    background-color: #FFF5DA;
  }</style>
</head>
<body>
<ul class="nav">
  <li>
    <a href="#">微博</a>
    <ul style="display:none">
      <li><a href="#">私信</a></li>
      <li><a href="#">评论</a></li>
      <li><a href="#">@我</a></li>
    </ul>
  </li>
  <li>
    <a href="#">留言板</a>
    <ul>
      <li>
        <a href="">私信</a>
      </li>
      <li>
        <a href="">评论</a>
      </li>
      <li>
        <a href="">@我</a>
      </li>
    </ul>
  </li>
  <li>
    <a href="#">电话</a>
    <ul>
      <li>
        <a href="">私信</a>
      </li>
      <li>
        <a href="">评论</a>
      </li>
      <li>
        <a href="">@我</a>
      </li>
    </ul>
  </li>
  <li>
    <a href="#">邮箱</a>
    <ul>
      <li>
        <a href="">私信</a>
      </li>
      <li>
        <a href="">评论</a>
      </li>
      <li>
        <a href="">@我</a>
      </li>
    </ul>
  </li>
</ul>
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</body>
</html>